If you need to locate a word within BP, you can use the search function of Notepad++ or you can opening the bp-languages/buddypress.pot file. There you can see the word and the name of the file(s) containing it, included the line #.

Hi,
you changed the wrong file. Never modify a core file when what you need is on the public side ! This means a template of the theme you’re using.
i said “you can search a term in the pot file”, not you must modify the pot file. This file is necessary for translation purpose and has no activity on your site. With a pot file you can generate a po file, and by saving it, you create the compiled mo file. PHP use this mo file at least.

How it works ?
– searching a word: xxx.pot file
– translating/modifying a word: xxx.po file (no T in the extension)
– saving the po file within a po editor sofware like poEdit
– saving the po file will generate a compiled format called .mo file witch must be uploaded on your server via FTP

In your case, the word “groups” you want to modify is used in these files. You will find this piece of code in your po file.